Electrical devices have become so common that without including lamps, it is not unusual for a home to have forty or fifty electrical devices. Many of these are portable and plug into convenience outlets although some are permanently wired. Typical plug-in devices include: clocks, hand tools, mixers, irons, toasters, electric razors, hair curlers, hair dryers, dehumidifiers and a wide variety of other devices. Most of the devices named use relatively little power with a maximum of the order of 1,000 watts. There are other devices which may use substantially more power such as: large room air conditioners, electric ranges, electric heaters, large ventilator fans and heavy duty power tools.
Every householder is very familiar with two types of problems relating to these portable devices. One problem is that through use, and sometimes misuse, the cord is pulled from its retaining means in the housing resulting in possible short circuits, loss of power and sometimes a fire hazard. Another problem which may result from use and possibly misuse is that the electric cord is bent at a sharp angle where it emerges from the device housing which may result in a break in the outer insulation and eventually the exposure of bare wires or possibly the fracturing of the internal wires through repeated bending.
In industrial application, wherein the present structure is expected to find its main utility, all the same problems exist and in addition, the structure is subject to mechanical abuses such as vibration and excessive tension and flexing forces as well as hostile environments such as exposure to water, oil and/or other industrial liquids and compounds.
The strain relief structure of this invention may be used to connect an electrical supply cord to outlet or junction boxes or panels on industrial equipment such as machine tools, outdoor illuminating devices, meter sockets, cranes and hoists, and a wide variety of portable machinery.
Many devices have been designed to try to prevent one or the other or both of these general difficulties and examination of almost any of the named devices will disclose a commercially used technique. The wide variety of devices in current use attests to the fact that no single device is suitable for all applications and/or that the ideal device remains to be designed.
U.S. Pat. No. 3,322,890 issued May 30, 1967 to J. C. Kennedy et al discloses a bushing seal fabrication from a deformable or ductile material such as nylon. Since the device is not fully threaded, it will exert radial forces and bind the wire positioned therein when the bushing device is threaded into a housing so that an unthreaded portion of the device is in the threaded area of the housing.
U.S. Pat. No. 3,352,961 issued Nov. 14, 1967 to H. Simon discloses another form of cable clamp which is formed of a plastic material having a plurality of jaws connected by relatively thin portions which are adapted to be compressed and urged into frictional engagement with the insulation of the wire and thereby hold the same in position against tension exerted on the wire. In some applications using structures having similar characteristics, the high unit pressures may tend to rupture the insulating jacket.
U.S. Pat. No. 3,796,504 issued Mar. 12, 1974 to G. A. G. Marechal teaches a clamping mechanism including jaws which are cammed into clamping relationship with the wire during assembly of the structure.
U.S. Pat. No. 4,095,043 issued June 13, 1978 to H. B. Martin et al discloses a technique wherein the wire is forced into a "U" shape in tightly confined quarters, thereby inhibiting movement of the wire in response to longitudinal forces.
U.S. Pat. No. 4,095,765 issued June 20, 1978 to M. Aimar discloses a cable clamp which may be used with a variety of cable diameters and which provides a pawl member which is brought into contact with the wire in response to the insertion and tightening of a screw.
U.S. Pat. No. 4,116,472 issued Sept. 26, 1978 to L. P. Schmitt discloses a body member having projecting legs which, as the assembly is tightened, are caused to pivot towards the centrally located wire and grasp same. To make the structure fluid tight, a membrane member is used.